If SR is given by:
Then this defaults to 1-a where a is the probability of death when the harmful intervention is applied and therefore has to be a constant.
Yes. This is why the survival ratio is constant across different baseline risks (given a specific, simple data generating mechanism that may occur when exposure increases risk of death). Importantly, no similar result exists for other measures of effect.
Do you think this is somehow an argument against the survival ratio? If so, you need to flesh out the argument and give me something to respond to